The invention relates to a system disconnector for physically disconnecting an upstream liquid system from a downstream liquid system.
System disconnectors or pipe disconnectors serve the purpose to safely prevent the backflow of liquid from a downstream liquid system to an upstream liquid system. The upstream liquid system may be a drinking water system. The downstream liquid system may be, for example, a heating system. It must be prevented under all circumstances, that contaminated water from the heating system flows back into the drinking water system when it is filled or re-filled, for example due to a pressure drop in the drinking water system for some reason. So called backflow preventers are known. These are spring biased valves allowing a liquid flow only in one direction, i.e. from the upstream to the downstream system. Such backflow preventers, however, can leak. Therefore, it is not permitted, for example with drinking water and heating water, to separate the liquid systems only by backflow preventers. A physical separation of the liquid systems must be effected in such a way, that in the case of a defect between the systems a connection to an outlet and the atmosphere is established.
System or pipe disconnectors comprise an upstream backflow preventer connected to the upstream liquid system and a downstream backflow preventer connected to the downstream system. A pressure controlled outlet valve is positioned between the backflow preventers, establishing the passage from the upstream liquid system to the downstream liquid system, if there is a sufficient pressure difference between the two liquid systems, so that the liquid can flow only from the upstream to the downstream liquid system. If there is no such pressure difference the outlet valve connects the space between the backflow preventers to the atmosphere and an outlet.